COMBINED INACTIVATION OF INTERFERON RESPONSE BY EPIGENETIC SILENCING AND JAK1 MUTATIONS RENDER TUMOR CELLS HYPER-SENSITIVE TO VIRAL INFECTION

The hormone-dependent LNCaP human prostate cancer cells were shown to extensive deregulate gene expression through epigenetic silencing. It was postulated that epigenetic silencing of Interferon Stimulated Genes (ISGs), including mediators of the Janus Kinase 1 (JAK1)/STAT1 transduction pathway, renders these cells hyper-susceptible to viral infections. However, recent findings show that JAK1 is mutated in LNCaP cells, providing additional basis for malfunction of the interferon pathway. Based on this, we asked the following questions: (i) Does abrogation of epigenetic silencing render LNCaP cells resistant to infection? (ii) Does IFN stimulation alter the cellular antiviral response in absence of JAK1 expression? (iii) Is IFN signaling in LNCaP cells dependent on abrogation of epigenetic silencing?

To address these questions we employed a mutant molecular clone of the human metapenumovirus expressing GFP (hMPV-GFP) as a marker of successful infection, which allows for quantitation of infection by fluorescent activated cell sorting and live cell microscopy. Abrogation of epigenetic silencing with inhibitors of DNA methyl transferases (5-Aza-deoxyCytidine or RG-108), of histone deacetylase inhibitors (trichostatin A) differentially enhanced the expression of a subset of ISGs, including IRF7. Notably these same treatments markedly reduced HMPV-GFP infection. Stimulation with IFN resulted in moderate increases in expression some ISGs, without reducing the susceptibility of LNCaP cells to hMPV-GFP. Combination of epigenetics-abrogating treatments and IFN stimulation further augmented the expression of this ISG subset (e.g., IRF7), while only moderately enhancing the infection-perturbing potential of the treatments alone. Our results identify the regulation of ISG expression in absence of canonical IFN signaling (JAK1/STAT), and underscore the role of silencing of anti-viral genes in cancer, with implications to combination therapy regimens employing both viruses and epigenetics-modifying compounds.